Confirming the efficacy/mechanism of an adaptive treatment for adolescent anorexia nervosa In adolescent anorexia nervosa (AN) 30-40% fully recover with Family Based Treatment (FBT) and remain so 3-4 years after treatment, but those who do not remit have a high risk of developing enduring AN with accompanying co-morbidities, much reduced quality of life, premature death, and for which there is no evidence-based treatment.Studies of FBT find that weight gain by session 4 predicts outcome in 85-90% of cases; thus, one way to improve outcomes in line with precision medicine is to match treatments to patients depending on weight gain at session 4 by offering an alternative treatment to meet the specific needs of poor early responders (~44%). The aim of this study in response to RFA-MH-16-425 is to determine if an adaptive outpatient treatment compatible with FBT could significantly improve outcomes by addressing poor early response and add to our understanding of the mechanisms of treatment in FBT. We developed a 3- session (Intensive Parent Coaching-IPC) intervention to increase parental skills at re-feeding for this poor early responding group demonstrating the feasibility of using a randomized adaptive design employing IPC. Compared to expected weight restoration rates in poor early responders, 50% more participants achieved weight restoration than expected with an average mean weight of 96.7% by EOT (preliminary efficacy signal of Cohen's d= 0.82). Previous studies have shown that FBT specifically targets parental self-efficacy as the mechanism to promote weight restoration in their children with AN.Consistent with these studies, data from the current pilot RCT suggest that parents whose children do not gain 2.4 kg by session 4 report lower levels of self-efficacy related to re-feeding as early as session 2; however, after receiving FBT+IPC, parental self- efficacy scores in this group improve and become indistinguishable from those of parents of early responders. While these preliminary data are promising, a sufficiently powered and controlled RCT using an adaptive randomized design employing FBT+IPC as the adaptive intervention for poor early responders is needed to understand the role of parental efficacy and re-feeding behaviors in FBT before recommending an adaptive approach. To conduct an adequately powered study (0.87 (alpha=.05, two-tailed)), 150 adolescents (75 per site) will be randomized at 2 sites (Stanford University and the University of California, San Francisco) to either standard FBT or an adaptive treatment arm (FBT+IPC) where those who do not gain 2.4 kg by session 4 will receive additional treatment (FBT+IPC). Assessments (blinded to treatment condition) will be conducted at baseline, 3, 9 (EOT) and at 6 and 12-month follow-up. Our primary outcome will be achievement of weight remission (>94% expected mean percent BMI adjusted for age, height and gender).